In particular in the motor vehicle sector, it is often necessary to join together steel sheets or plates by welding. In this context, a corresponding weld seam is typically produced at a joint between two sheets which are to be joined together. Nowadays, a laser is often used for producing the weld seam. For the quality of the weld seam produced, it is of decisive importance that the laser beam of the laser exactly follows the joint or the gap between the sheets which are to be joined, that is to say a corresponding lateral offset between an actual weld seam path and a target weld seam path is kept to a minimum.
The prior art provides various solutions for keeping the lateral offset to a minimum.
A first solution provides gripping the sheets which are to be joined in a welding device very exactly and always displacing the laser in the same manner relative to the welding device so as to produce the weld seam. This is a cost-effective approach, since no electronics are required for monitoring the lateral offset. However, a drawback is that tolerances in the geometry of the sheets which are to be joined, or indeed tolerances which result from slightly different gripping positions of the sheets in the welding device, cannot be compensated. There may thus even be a large lateral offset in some cases.
Further solutions for minimising the lateral offset are disclosed for example in document DE 691 27 121 T2. A solution disclosed therein provides the use of contact probes, which follows the joint between the two sheets. However, contact probes of this type often lose contact with the corresponding joint, placing the quality of the weld seam at risk. In general, systems of this type are limited to low welding speeds and special applications. Moreover, the contact probes are sensitive to heat and wear, and this can result in them failing.
DE 691 27 121 T2 further discloses a visual detection system, which detects and corrects the actual weld seam path in comparison with the component position. Systems of this type have the drawback of being very complex and thus cost-intensive.